It sounds like your just trying to keep up with your friends. Thats great, if you have enough money to do that. If you don't, your going to go broke trying. Better video card will provide better frame rates, so if you TRUELY aren't happy with what you have, you should get another one. (did you ever list system specs? You might have a different bottleneck then the GPU)
If the 4380 is in your price range, get it. Its better then the other cards you've listed. Yes the 4870/4890 are great cards, but they cost to much. (for you)